The present invention relates to a foamable vinyl chloride-based resin composition or, more particularly, to a vinyl chloride-based resin composition capable of foaming into a cellular porous body of the resin having a beautiful appearance with metallic luster of the surface.
As is well known, vinyl chloride-based resins are outstandingly inexpensive in comparison with othr syntheric resins and capable of being molded easily into a variety of shaped articles along with the development of the technology of molding in recent years. Shaped articles of vinyl chloride-based resins have well-balanced mechanical properties and high flame retardancy so that they are widely used in various fields of applications as a building material, wrapping material and the like. Typical examples of the shaped articles of vinyl chloride-based resins include pipes, corrugated boards, decking boards, window frames, sheets and the like with the rigid-type formulations of the resin composition and films, insulation of electric wires, miscellaneous goods and others with the flexible-type formulations of the resin composition containing a plasticizer.
As a trend in recent years, a rapidly increasing proportion of the shaped articles of vinyl chloride-based resins is directed to those having cellular porous structure by foaming a foamable resin composition with an object of weight decrease and increase in the heat insulation as well as decrease of the cost for a unit volume of the shaped article. The demand for such foamed products is directed more and more to shaped articles having higher commercial values not only in the performance in use but also in the aesthetic appearance thereof. For example, shaped articles of a vinyl chloride-based resin having metallic surface finish are preferred in the market with their lustrous appearance and massiveness. Such a metallic-finished article is manufactured usually by plating of a pre-shaped article with a metal or by lamination of a metal-deposited film. The method of metal plating on a plastic-made article is naturally under limitations by the material of the substrate plastic and the process of plating on a plastic substrate is complicated with low productivity so that the method is not widely accepted for the purpose with the considerbly high cost of the products. The laminating method with a metal-deposited film is also not free from several problems that an expensive laminating machine is indispensable, the process involves an increased nuumber of steps, the yield of acceptable products is not always high enough due to the meandering of the film in the course of lamination and the laminated film is sometimes exfoliated to expose the substrate surface before or during use of the article resulting in a greatly decreased commercial value of the product.